Implement base::PowerMonitor::IsOnBatteryPower() for OSX.

base/power_monitor/power_monitor_device_source_ios.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/power_monitor/power_monitor_device_source.h"
 
 #import <UIKit/UIKit.h>
 
 namespace base {
 
+bool PowerMonitorDeviceSource::IsOnBatteryPowerImpl() {

[Nico, 2016/09/27 20:19:27]

Is this used by anything on iOS? If not, maybe we can not provide an
implementation so we'll get a link error if something starts using it. If it is
used on iOS, there should probably be a bug about for implementing it.

[DaleCurtis, 2016/09/27 20:53:42]

ios_chrome_unittests fails to link without this, but I haven't found anything
using it explicitly. See any of the previous patch set try jobs for more
details. Here's the exact error w/o this for posterity:

FAILED: obj/ios/chrome/arm/ios_chrome_unittests 
...
Undefined symbols for architecture armv7:
  "base::PowerMonitorDeviceSource::IsOnBatteryPowerImpl()", referenced from:
      vtable for base::PowerMonitorDeviceSource in
libbase.a(power_monitor_device_source.o)

https://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/build...

+  NOTIMPLEMENTED();
+  return false;
+}
+
 void PowerMonitorDeviceSource::PlatformInit() {
   NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
   id foreground =
       [nc addObserverForName:UIApplicationWillEnterForegroundNotification
                       object:nil
                        queue:nil
                   usingBlock:^(NSNotification* notification) {
                       ProcessPowerEvent(RESUME_EVENT);
                   }];
   id background =
@@ skipping 10 matching lines @@
 void PowerMonitorDeviceSource::PlatformDestroy() {
   NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
   for (std::vector<id>::iterator it = notification_observers_.begin();
        it != notification_observers_.end(); ++it) {
     [nc removeObserver:*it];
   }
   notification_observers_.clear();
 }
 
 }  // namespace base